The following document lists the file abstract/DLAMBERT_DLL002.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
Analyses of photospheric spectra of stars are vital tools for our understanding of issues from the origin of the Universe, the evolution of the Galaxy to the lives of stars. Contemporary analyses of spectra depend on model stellar atmospheres computed usually from a set of simplifying assumptions: plane-parallel homogeneous layers in radiative/convective hydrostatic and local themodynamic equilibrium. Only few attempts have been made to derive atmospheric structures as direct as possible from observations, i.e. to construct empirical atmospheres. With new observational methods, and new wavelength regions opening up, it is very important to try such methods. In this respect the infrared spectral region offers new and unique possibilities. This proposal considers such atmospheres of cool dwarf stars whose chemical compositions are unique clues to the early evolution of the Galaxy. The study is motivated by the power of ISO photometry to measure the temperature in the upper photospheric layers: the opacity in the infrared is provided by the free-free transitions of the H- ion and scales as wavelength-squared. Hence, a large range of depths is sampled by the flux between 3 to 120 micron. Previous studies of optical line and continuous spectra suggest that theoretical model atmospheres do not yet adequately represent the real atmospheres of cool dwarf stars. This is the case, for instance, of the very metal-poor star HD140283 for which standard model atmospheres with usual mixing length values seem to be unable to provide simultaneous fits to the H Alpha and Beta lines, and show a temperature distribution which is considerably hoter than that predicted by theoretical models in the lower layers. These inadequacies also motivate the study.